+#include <stdlib.h>
+
+#include "libthreads.h"
+#include "schedule.h"
+#include "common.h"
+#include "threads_internal.h"
+
+/* global "model" object */
+#include "model.h"
+
+#define STACK_SIZE (1024 * 1024)
+
+static void *stack_allocate(size_t size)
+{
+ return malloc(size);
+}
+
+static void stack_free(void *stack)
+{
+ free(stack);
+}
+
+Thread *thread_current(void)
+{
+ return model->scheduler->get_current_thread();
+}
+
+int Thread::create_context()
+{
+ int ret;
+
+ ret = getcontext(&context);
+ if (ret)
+ return ret;
+
+ /* start_routine == NULL means this is our initial context */
+ if (!start_routine)
+ return 0;
+
+ /* Initialize new managed context */
+ stack = stack_allocate(STACK_SIZE);
+ context.uc_stack.ss_sp = stack;
+ context.uc_stack.ss_size = STACK_SIZE;
+ context.uc_stack.ss_flags = 0;
+ context.uc_link = &model->system_thread->context;
+ makecontext(&context, start_routine, 1, arg);
+
+ return 0;
+}
+
+int Thread::swap(Thread *t)
+{
+ return swapcontext(&this->context, &t->context);
+}
+
+void Thread::dispose()
+{
+ DEBUG("completed thread %d\n", thread_current()->get_id());
+ state = THREAD_COMPLETED;
+ stack_free(stack);
+}
+
+int Thread::switch_to_master(ModelAction *act)
+{
+ Thread *next;
+
+ DBG();
+ model->set_current_action(act);
+ state = THREAD_READY;
+ next = model->system_thread;
+ return swap(next);
+}
+
+Thread::Thread(thrd_t *t, void (*func)(), void *a) {
+ int ret;
+
+ user_thread = t;
+ start_routine = func;
+ arg = a;
+
+ /* Initialize state */
+ ret = create_context();
+ if (ret)
+ printf("Error in create_context\n");
+
+ state = THREAD_CREATED;
+ model->assign_id(this);
+ model->scheduler->add_thread(this);
+}
+
+Thread::Thread(thrd_t *t) {
+ /* system thread */
+ user_thread = t;
+ state = THREAD_CREATED;
+ model->assign_id(this);
+ create_context();
+ model->add_system_thread(this);
+}
+
+thread_id_t Thread::get_id()
+{
+ return thrd_to_id(*user_thread);
+}
+
+/*
+ * Return 1 if found next thread, 0 otherwise
+ */
+static int thread_system_next(void)
+{
+ Thread *curr, *next;
+
+ curr = thread_current();
+ model->check_current_action();
+ if (curr) {
+ if (curr->get_state() == THREAD_READY)
+ model->scheduler->add_thread(curr);
+ else if (curr->get_state() == THREAD_RUNNING)
+ /* Stopped while running; i.e., completed */
+ curr->dispose();
+ else
+ DEBUG("ERROR: current thread in unexpected state??\n");
+ }
+ next = model->scheduler->next_thread();
+ if (next)
+ next->set_state(THREAD_RUNNING);
+ DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
+ if (!next)
+ return 1;
+ return model->system_thread->swap(next);
+}
+
+static void thread_wait_finish(void)
+{
+
+ DBG();
+
+ while (!thread_system_next());
+}
+
+/*
+ * Main system function
+ */
+int main()
+{
+ thrd_t user_thread, main_thread;
+ Thread *th;
+
+ model = new ModelChecker();
+
+ th = new Thread(&main_thread);
+
+ /* Start user program */
+ thrd_create(&user_thread, &user_main, NULL);
+
+ /* Wait for all threads to complete */
+ thread_wait_finish();
+
+ model->print_trace();
+ delete th;
+ delete model;
+
+ DEBUG("Exiting\n");
+ return 0;
+}